The Case of the Buried Necklace

Ava Wilder, Noah Carter, Lizzie Cooper, and Ethan White are best friends. The 4 twelve-year-olds created their own business called The Grass Busters and are spending their summer vacation mowing lawns to earn spending money for their beach trip in August.
While mowing a neighbors lawn, they discover an emerald necklace half buried in the dirt. They discover the original owner disappeared years ago. Can they solve the mysterious disappearance and still earn enough money for their vacation?